On his statement—“they are swimming”—he said, “They revolve through the portals of heaven just as the spindle revolves within its whorl.”

He also related: al-Ḥasan ibn al-Ḥasan reported to us, saying, Ibrāhīm ibn ʿAbd Allāh al-Harawī narrated to us, Ḥajjāj narrated to us from Abū Juʿayj, who said: ʿAbd Allāh ibn Kathīr informed me that he heard Mujāhid say about the verse, ‘and each one is swimming along in its orbit’ (Q 36:40): “The stars, the sun, and the moon move in a whorl like the whorl of a spindle.” He added, “Likewise the ḥusbān”—Mujāhid meant the pin of a millstone—“resembles the pin on which the millstone turns.” In classical Arabic, ḥusbān denotes short arrows, the singular of which is ḥusbānah. Mujāhid used this image to explain the verse, ‘The sun and the moon [run] according to ḥusbān’ (Q 55:5). Others, however, said the word is derived from ḥisāb (reckoning); some considered it a verbal noun, while others held it to be the plural of ḥisāb, analogous to shihāb and shuhbān.

Mujāhid further said, “The spindle cannot turn without its whorl, nor can the whorl turn without the spindle; the pin cannot turn without the millstone, nor the millstone without the pin. In the same way, the stars, the sun, and the moon are in an orbit that cannot persist without it, nor can it persist without them.” He then tapped with his finger, whereupon Mujāhid remarked, “They revolve just like this tap.” He concluded, “The ḥusbān and the falak amount to one and the same concept, except that ḥusbān is used for the millstone while falak is used for the spindle.” All of this is from Mujāhid.

I say: His expression ‘it cannot persist without it’ means ‘it cannot revolve except by means of it.’ From this comes the term dawāmah (with ḍammah and tashdīd), the little whorl a boy flicks with a string so that it spins on the ground—that is, revolves. The same root lies behind tadwīm al-ṭayr, the circling of a bird as it rises into the sky. As for the phrase ‘he tapped with his finger,’ it means he struck it against the ground and set it spinning to illustrate the revolution of the heavenly sphere.

Ibn Abī Ḥātim said: It was read aloud to Yūnus ibn ʿAbd al-Aʿlā—who reported from Ibn Wahb, from al-Sarī ibn Yaḥyā—that a man once asked al-Ḥasan al-Baṣrī about the verse, ‘Each one is swimming along in its orbit.’